S91

S91 may refer to:


 * S91 (New York City bus), serving Staten Island
 * "S91" (song), a 2023 song by Colombian singer Karol G
 * Blériot-SPAD S.91, a French biplane fighter
 * County Route S91 (Bergen County, New Jersey)
 * Daihatsu Zebra (S91), a pickup truck and van
 * HMS Trenchant (S91), a submarine of the Royal Navy
 * SIPA S.91, a French trainer aircraft